The parenchymella larva of H. hamigera owns 8 different cellular types: collencytes, spherulous cells, urn-shaped cells, cells of posterior pole, and flagellar cells. During the metamorphosis, urn-shaped cells and cells of posterior pole disappear; pinacocytes are issued from collencytes and archaeocytes; and the grey-cells differentiate from flagellar cells as well as the choanocytes.